[D] Brontomerus mcintoshi [sG] [T]
Taylor Wedel & Cifelli 2011
Cretaceous Early Aptian Albian
Saurischia Sauropodomorpha Sauropoda Camarasauridae
Cedar Mountain Formation, Top of the Ruby Ranch Member, Hotel Mesa Quarry (OMNH locality V857), Grand County, eastern Utah, US
Brontomerus mcintoshi is a new genus and species of sauropod dinosaur from the Hotel Mesa Quarry in Grand County, Utah, USA, in the upper part of the Ruby Ranch Member (Aptian–Albian) of the Lower Cretaceous Cedar Mountain Formation. It is known from at least two fragmentary specimens of different sizes. The type specimen is OMNH 66430, the left ilium of a juvenile individual; tentatively referred specimens include a crushed presacral centrum, a complete and well preserved mid to posterior caudal vertebra, the partial centrum of a distal caudal vertebra, a complete pneumatic anterior dorsal rib from the right side, the nearly complete left scapula of a much larger, presumably adult, individual, and two partial sternal plates.
Brontomerus is diagnosed by five autapomorphies of the type specimen: preacetabular lobe 55% of total ilium length, longer than in any other sauropod; preacetabular lobe directed anterolaterally at 30o to the sagittal, but straight in dorsal view and vertically oriented; postacetabular lobe reduced to near absence; ischiadic peduncle reduced to very low bulge; ilium proportionally taller than in any other sauropod, 52% as high as long. In a phylogenetic analysis,
Brontomerus was recovered as a camarasauromorph in all most parsimonious trees, but with uncertain position within that clade. The large preacetabular lobe of the ilium anchored powerful protractor and abductor muscles, but precise interpretation is impossible without functionally related elements such as femora and proximal caudal vertebrae.
Brontomerus is the eighth sauropod genus named from the Early Cretaceous of North America, and more remain to be described: North American sauropod diversity did not decline catastrophically at the end of the Jurassic as often assumed. The most striking differences between Late Jurassic and Early Cretaceous sauropod faunas in North America is that the former are abundant and dominated by diplodocids, whereas the latter are comparatively scarce though still diverse and dominated by macronarians.
From Greek bronto, thunder; Greek merós, thigh; “thunder−thighs”, in reference to the substantial femoral musculature implied by the morphology of the ilium. In honor of veteran sauropod worker John S. McIntosh, whose seminal paleontological work, done mostly unfunded and on his own time, has been an inspiration to all of us who follow .
OMNH 66430, a left ilium.
Tentatively referred material
OMNH 66429, crushed presacral centrum; OMNH 61248, mid−to−posterior caudal vertebra; OMNH 27794, partial distal caudal centrum; OMNH 27766, anterior right dorsal rib; OMNH 27761, nearly complete left scapula missing anterior portion; OMNH66431 and 66432, two partial sternal plates; and other fragments.
Hotel Mesa Quarry (OMNH locality V857), Grand County, eastern Utah, US
Top of the Ruby Ranch Member of the Cedar Mountain Formation (Lower Cretaceous, Aptian–Albian)
Preacetabular lobe 55% of total ilium length, longer than in any other sauropod; preacetabular lobe directed anterolaterally at 30o relative to the sagittal plane, but straight in dorsal view and vertically oriented; postacetabular lobe reduced to near absence; ischiadic peduncle reduced to very low bulge; ilium proportionally taller than in any other sauropodheight is 52% of total length, compared with a maximum of 45% in other sauropods.
If the tentatively referred elements do belong to the same species as the holotype, then the following additional characters also diagnose the new taxon: presacral vertebrae camellate; mid−to−posterior caudal vertebrae with elongate pre and postzygapophyseal rami, having the postzygapophyseal facets hanging below the level of the ramus; first dorsal rib with expanded, dorsally oriented articular facets, laterally curving shaft, and ventrally directed pneu matic foramen in head; acromion expansion of scapula pronounced and steep, but not forming acromion fossa; dorsal and ventral margins of scapular blade “stepped”; sternal plates crescentic, and three times as long as broad.
Unambiguous autapomorphies distinguishing Brontomerus from the root of the polytomy in which it is recovered in the strict consensus of most parsimonious trees in the phylogenetic analysis below: character 184, ratio of centrum length:height in middle caudal vertebrae _> 2.0; 185, sharp ridge on lateral surface of middle caudal centra at archbody junction absent; 212, posterior end of scapular body racquet−shaped (dorsoventrally expanded); 261, in lateral view, the most anteroventral point on the iliac preacetabular lobe is also the most anterior point (preacetabular lobe is pointed); 264, projected line connecting articular surfaces of ischiadic and pubic peduncles of ilium passes ventral to ventral margin of postacetabular lobe of ilium.